GNGTS 2017 - 36° Convegno Nazionale

GNGTS 2017 S essione 2.1 247 magnitude Mw (Hanks and Kanamori, 1979), based on an estimate of the seismic moment (Aki, 1968; Kanamori and Anderson, 1975), provides fault-averaged, low-frequency information about the source processes, but relatively less information about the small-wavelength high- frequency rupture details (e.g., Beresnev, 2009). On the other hand, since the energy magnitude Me (Choy and Boatwright, 1995; Choy and Kirby, 2004) is based on an estimate of the radiated energy E R , it is linked to the source dynamics and is more sensitive to high-frequency source details (e.g., variations of the slip and/or stress conditions, and the dynamic friction at the fault surface during the rupture process). Me was introduced by Choy and Boatwright (1995) using teleseismic broadband P-wave recordings, and an automatic procedure for its estimation is available (Di Giacomo et al. , 2010). At local distances, several approaches for computing E R have been proposed (e.g., Thatcher and Hanks, 1973; Cocco and Rovelli, 1989; Kanamori et al. , 1993; Singh and Ordaz, 1994). In these studies, E R was computed from S-wave signals corrected for a suitable parametric attenuation model (e.g., Kanamori et al. , 1993), or from a source spectrum that was obtained by jointly inverting a set of local recordings for the source, attenuation and site contributions (e.g., Zollo et al. , 2014). Recently, Picozzi et al. (2017) have presented a new P-wave procedure for the rapid assessment of Me at local scale aiming at its future implementation within earthquake early warning systems. The authors considered the squared velocity integral parameter IV2 (Festa et al. , 2008) computed for P-waves as proxy for the estimation of E R , which in turn was used to define a new magnitude scale (i.e., energy-based local magnitude, MLe). The P-wave based approach was divided in two steps: first an empirical attenuation function with distance of E R and an empirical relationship between ML and E R were derived, considering 29 earthquakes with Mw > 4 belonging to the L’Aquila (2009) seismic sequence in central Italy, and to the Emilia (2012) sequence in northern Italy. Then, the procedure was applied to 39 earthquakes of the 2016, central Italy seismic sequence. In this study, we extend the approach proposed by Picozzi et al. (2017) from P- to S-waves to introduce a new procedure for providing, in real-time, robust estimates of E R , seismic moment (Mo), and scaled energy [i.e., log(E R /Mo)] in central Italy. We first calibrate empirical attenuation functions between proxies for E R and Mo measured on direct S-waves, analysing more than 200 earthquakes with Mw > 2 occurred in central Italy before the 2016, Mw 6.0Amatrice earthquake. Then, we derive two empirical scaling relationships: the first one between E R and Mle and the second one between Mo and a rapid-response moment magnitude scale (referred to as M Wrr ). Finally, we present the results obtained applying the procedure to a large dataset of about 770 earthquakes with Mw > 2 occurred in central Italy in the period 2016 to 2017. We envisage that M Le and M Wrr can in the next future be routinely computed by local networks for the real-time estimation of the earthquake size. Furthermore, rapid estimates of scaled energy provide the information necessary for the real-time identification of earthquakes characterized by a higher proportion of energy being transferred to seismic waves, and therefore, providing important real-time indications of earthquakes shaking potential. References Aki, K.; 1968: Seismic displacements near a fault . J. Geophys. Res., 73, 16, 5359–5376, doi:10.1029/ JB073i016p05359. Beresnev, I. A.: 2009: The reality of the scaling law of earthquake-source spectra? . J. Seismol., 13, 433–436, doi:10.1007/s10950-008-9136-9. Bormann, P., Wendt, S., and Di Giacomo, D.; 2013: Seismic Sources and Source Parameters. In: Bormann, P. (Ed.), New Manual of Seismological Observatory Practice 2 (NMSOP2), Potsdam: Deutsches GeoForschungsZentrum GFZ, pp. 1—259. doi: http://doi.org/10.2312/GFZ.NMSOP-2_ch3. Choy, G. L., and Boatwright J.; 1995: Global patterns of radiated seismic energy and apparent stress . J. Geophys. Res. 100, 18,205–18,226. Choy, G. L., and Kirby, S.; 2004: Apparent stress, fault maturity and seismic hazard for normal-fault earthquakes at subduction zones . Geophys. J. Int., 159, 991-1012.